Effectiveness of a new tobramycin (0.3%) and dexamethasone (0.05%) formulation in the treatment of experimental Pseudomonas keratitis.

OBJECTIVE

To quantitatively determine, in a Pseudomonas keratitis model, the anti-inflammatory and bactericidal properties of a new formulation of tobramycin (0.3%) and dexamethasone (0.05%) that utilizes a xanthan gum vehicle.

RESEARCH METHODS

In a randomized and masked fashion, rabbit corneas (n>/=16 eyes per group) were intrastromally injected with 10(3) colony-forming units (CFU) of P. aeruginosa. Eyes were untreated or were administered a single drop every 15 min between 16 and 17 h postinfection (PI) and then a single drop every 30 min between 17 and 22 h PI, a total of 15 drops of either 0.1% dexamethasone and 0.3% tobramycin (TobraDex; Tdex) or a new formulation 0.3% tobramycin and 0.05% dexamethasone with xanthan gum (TobraDex ST; ST). Slit lamp examination scores (SLE+/-SEM) were derived from grading seven parameters at 22 h PI. Rabbits were sacrificed at 23 h PI and the log CFU+/-SEM per cornea was determined.

RESULTS

Untreated eyes had SLE scores of 11.11+/-0.43 and had log CFU of 7.27+/-0.06. Eyes treated with Tdex, as compared to the untreated eyes, had significantly lower SLE scores (7.39+/-0.21, p<0.0001) and significantly fewer bacteria (6.32+/-0.29 log CFU, p=0.0213). Eyes treated with ST had a SLE score (6.56+/-0.19) that was significantly lower than both the untreated eyes (p<0.0001) and the eyes treated with Tdex (p=0.0124). Furthermore, eyes treated with ST had significantly fewer log CFU (5.78+/-0.30) than untreated eyes (p=0.0001) or eyes treated with Tdex (p=0.0434).

CONCLUSIONS

The ST formulation with xanthan gum demonstrated statistically superior anti-inflammatory and bactericidal properties as compared to Tdex.

LIMITATIONS

Variations in inoculation procedures produced limited eye-to-eye differences in the infection.